Ester of the 1-methyl-5-p-toluoylpyrrole-2-acetic acid having antiinflammatory, mucolytic and antitussive properties, process for its preparation and pharmaceutical compositions containing them

ABSTRACT

1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester, which possesses antiinflammatory, antipyretic, mucolytic and antitussive properties, is disclosed. 
     This ester is prepared by reacting guaiacol with an activated derivative of the 1-methyl-5-p-toluoylpyrrole-2-acetic acid of formula ##STR1## wherein X is an activating group suitable for promoting the formation of an ester bond.

The present invention relates to 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester having formula ##STR2## which possesses valuable antiinflammatory, analgesic antipyretic, mucolytic and antitussive properties.

The present invention also relates to a process for preparing this ester and to orally or parenterally administrable pharmaceutical compositions containing same. This compound is very effective in the treatment of any pathological conditions, whether acute or chronic, of the upper airways when these are affected by inflammatory and catarrhal conditions and accompanied by pain and fever.

The ester of this invention can be prepared by esterifying 1-methyl-5-p-toluoylpyrrole-2-acetic acid with guaiacol (2-methoxyphenol) in the presence of a suitable condensing agent and, optionally, of a catalyst.

More specifically, the process of this invention comprises:

reacting guaiacol with an activated derivative of the 1-methyl-5-p-toluoylpyrrole-2-acetic acid of general formula ##STR3## wherein X is an activating group suitable for promoting the formation of an ester bond with guaiacol at a temperature comprised between about 0° C. and 35° C., in the presence of either aprotic or protic solvents depending on the nature of the activating group

Suitable activated derivatives of formula ##STR4## are those wherein X is selected from the group consisting of the halogen atoms (preferably chlorine), the ##STR5## residue, wherein R₆ and R₇ are alkyl radicals having from 1 to 3 carbon atoms or cycloalkyl radicals having from 5 to 6 carbon atoms, preferably cyclohexyl, and the ##STR6## residue.

All these activated derivatives can be prepared by well-known procedures.

When X is halogen (e.g. chlorine), the corresponding activated derivative can be prepared by halogenating (e.g. chlorinating) 1-methyl-5-p-toluoylpyrrole-2-acetic acid.

When X is the ##STR7## residue (preferably, R₆ =R₇ =cyclohexyl), the corresponding activated derivative is prepared by condensing 1-methyl-5-p-toluoylpyrrole-2-acetic acid with an N,N'-dialkylcarbodiimide (preferably, N,N'-dicyclohexylcarbodiimide). This condensation reaction can be suitably carried out in the presence of a catalyst, such as p-toluensulfonic acid, 4-dimethylaminopyridine and 4-(1-pyrrolidinyl) pyridine.

When X is the ##STR8## residue, the corresponding activated derivative is prepared by condensing 1-methyl-5-p-toluoylpyrrole-2-acetic acid with N,N'-carbonyldiimidazole. This condensation reaction can be suitably carried out in the presence of a catalyst, such as sodium or magnesium ethylate.

The process is generally carried out in a nonpolar environment, although water-dioxane and water-tetrahydrofuran mixtures can be employed with N,N'-dicyclohexyl-carbodiimide is used as condensing agent, in the presence or absence of a catalyst. Preferred solvents are the following: dichloromethane, dichloroethane, tetrahydrofuran, dioxane, dimethyl-sulfoxide and N,N-dimethylformamide.

The preparation of the ester according to this invention is illustrated by the following example.

EXAMPLE Preparation of 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester

To a solution of 5.14 g (0.02 mole) of 1-methyl-5-p-toluoylpyrrole-2-acetic acid in 200 ml of dichloromethane, cooled on an ice bath and kept under vigorous stirring, there was firstly added a solution of 4.4 g (0.022 moles) of dicyclohexylcarbodiimide in 40 ml of dichloromethane, then a solution of 2.8 g (0.024 moles) of guaiacol in 40 ml of the same solvent and, finally, a solution of 300 mg of 4 (1-pyrrolidinyl) pyridine in 40 ml of dichloromethane. The resulting mixture was kept under stirring at 0°C.-5° C. for 0.5 hour, then under stirring at room temperature for 3.5 hours.

The precipitate of N,N'-dicyclohexylurea which formed (4 g) was filtered off and the filtrate was evaporated under vacuum. The residue was taken up with ethyl acetate (300 ml) and the organic solution was transferred into a separatory funnel and first washed with a solution of 5% acetic acid (50 ml) to remove the catalyst, then with 2N NaOH (2×25 ml) to remove the unreacted starting acid and guaiacol, and finally washed with a saturated solution of sodium chloride till neutrality. After drying on anhydrous sodium sulfate, the mixture was filtered and the solvent removed under vacuum. An oil was obtained, which was chromatographed on silica using benzene as eluant. After solvent removal from the collected eluates, about 5.5 g of a yellowish oil were obtained, which solidified spontaneously. This product, taken up with a small amount of cyclohexane and filtered, gave a colourless solid product (5 g; 69.4% of the theoretical value) having melting point 95°-96° C. After crystallization from cyclohexane, an analysis sample of 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester had melting point 98°-99° C.

Analysis: C₂₂ H₂₁ NO₄ ; calculated % C 72.71; H 5.82; N 3.85. found % C 72.79; H 5.81; N 4.00.

corresponding to the compound having formula ##STR9##

Its chemico-physical characteristics are as follows:

Empyrical formula: C₂₂ H₂₁ NO₄

Molecular weight: 363.40

Melting point: 98°-99° C. (from cyclohexane)

Yield: 69.4% of the theoretical value

Solubility: soluble in the usual organic solvents

IR and NMR spectra confirm that this ester compound possesses the above-identified structure.

PHARMACOLOGICAL PROPERTIES

The experiments carried out with the 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester show that this product possesses pharmacological properties suitable for therapeutic application in some pathological conditions. The composition that had been administered via the oral and/or parenteral route, was in suspension of 0.5% carboxymethylcellulose in neutral pH physiological saline solution. In particular the compound of this invention exhibited an inhibiting action against acute inflammation concomitantly to a marked analgesic action. It has also been demonstrated, as described below, that this compound has a considerable antithermic activity, and in vivo tests show good mucolytic and antitussive activity. All these pharmacotherapeutic effects were obtained with doses and administration regimens that did not provoke significant toxic effects. It was also shown that this compound can be perfectly tolerated by the gastrointestinal tract. Doses, the routes of administration and in general the methods whereby the effects on animals are obtained suggest that this compound can be useful in human therapy for pathological situations characterized by phlogosis and pain. As an example the experimental data are described below of the activity of the compound of this invention compared with that of the 1-mehtyl-5 -p-toluoyl-2-acetic acid sodium salt dihydrate (tolmetin Na.2H₂ O), at equimolecular doses, and also with that of indomethacin in the antiinflammatory test.

Antiinflammatory activity

This effect was evaluated by means of an experimental model reproducing acute inflammation in rats: for this purpose the carrageenin-induced oedema test was employed following the method described by C. A. Winter (J. Pharmac. Exp. Ther. 141: 369, 1963) using as reference substances of known antiinflammatory acitivity: indomethacin and tolmetin Na.2H₂ O S. Wong, J. F. Gardocki and T. P. Pruss, J. Pharmac. Exp. Ther. 185 (1): 127, 1973).

Table I lists the tested compounds, the concentration thereof, routes of administration and relative percentage oedema inhibitions; the data are commented upon at the end of the Tables.

                                      TABLE I                                      __________________________________________________________________________     Antiinflammatory activity of 1-methyl-5-p-toluoylpyrrole-2-                    acetic acid guaiacyl ester                                                                    OEDEMA % INHIBITION                                                        DOSE                                                                               per os      i.p.                                                COMPOUNDS  mg/kg                                                                              2 h                                                                               4 h                                                                               6 h                                                                               24 h                                                                              2 h                                                                               4 h                                                                               6 h                                                                               24 h                                       __________________________________________________________________________     Indomethacin                                                                              2.5 18.6                                                                              20.7                                                                              19.2                                                                              2.6                                                                               21.0                                                                              20.0                                                                              17.0                                                                              2.5                                        "          5   26.3                                                                              29.1                                                                              28.5                                                                              2.7                                                                               30.0                                                                              29.0                                                                              23.0                                                                              3.4                                        "          10  48.2                                                                              49.0                                                                              46.0                                                                              7.9                                                                               49.7                                                                              46.0                                                                              48.1                                                                              8.0                                        Tolmetin Na.2H.sub.2 O                                                                    25  24.6                                                                              26.2                                                                              30.1                                                                              6.2                                                                               28.0                                                                              29.1                                                                              32.1                                                                              8.9                                        "          50  43.1                                                                              46.0                                                                              41.3                                                                              9.1                                                                               47.0                                                                              49.1                                                                              40.0                                                                              7.1                                        "          100 60.8                                                                              60.0                                                                              64.5                                                                              14.6                                                                              64.1                                                                              65.8                                                                              60.2                                                                              11.2                                       1-methyl-5-p-toluoyl-                                                                     25  27.0                                                                              29.0                                                                              28.0                                                                              3.2                                                                               33.5                                                                              30.0                                                                              25.0                                                                              7.0                                        pyrrole-2-acetic                                                                          50  49.0                                                                              53.0                                                                              51.0                                                                              5.3                                                                               55.0                                                                              51.6                                                                              49.0                                                                              9.2                                        acid guaiacyl ester                                                                       100 71.6                                                                              77.8                                                                              77.0                                                                              7.2                                                                               80.0                                                                              78.0                                                                              70.0                                                                              9.5                                        __________________________________________________________________________

Analgesic activity

By means of the phenylquinone-induced writhing test (abdominal contractions) described by E. Siegmund (Proc. Soc. Exp. Biol. Med. 95: 729, 1957) the analgesic activity of 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester was evaluated.

The inhibiting effect on the abdominal contractions induced by phenyl-p-quinone was calculated by the following formula: ##EQU1##

Table II lists the doses, routes of administration and their efficacy expressed as percentage of protection.

                  TABLE II                                                         ______________________________________                                         Analgesic activity of 1-methyl-5-p-toluoyl-                                    pyrrole-2-acetic acid guaiacyl ester                                                       DOSE    % PROTECTION                                               COMPOUNDS     mg/kg     per os   i.p.                                          ______________________________________                                         Vehicle       --        0.0      0.0                                           Tolmetin Na.2H.sub.2 O                                                                        5        15.0     16.5                                          "             10        40.6     46.2                                          "             20        62.0     69.1                                          1-methyl-5-p-toluoyl                                                                          5        30.0     30.0                                          pyrrole-2-acetic                                                                             10        58.6     62.5                                          acid guaiacyl ester                                                                          20        79.4     78.0                                          ______________________________________                                    

Antipyretic activity

In order to determine this activity, hyperthermia was induced in albino male Wistar rats weighing 250±10 g by intraperitoneally injecting 10 ml/kg of a 1.5% suspension of dry, purified brewer' yeast (Carlo Erba). The substance used for comparison was tolmetin Na.2H₂ 0 the antipyretic activity whereof is well known (S. Wong, S. F. Gardocki and T. P. Pruss, J. Pharmac. Exp. Ther. 185(1): 127, 1973).

                  TABLE III                                                        ______________________________________                                         Antipyretic activity of 1-methyl-5-p-toluoyl-                                  pyrrole-2-acetic acid guaiacyl ester                                                        % temperature decrease                                                    DOSE   per os       i.p.                                               COMPOUNDS mg/kg    1 h    2 h  3 h  1 h  2 h  3 h                              ______________________________________                                         Tolmetin  50       12.0   20.0 29.5 15.0 19.0 30.5                             Na.2H.sub.2 O                                                                  Tolmetin  75       13.0   26.0 27.0 18.0 29.0 34.0                             Na.2H.sub.2 O                                                                  Tolmetin  100      18.0   30.9 47.0 28.0 39.0 51.0                             Na.H.sub.2 O                                                                   1-methyl-5-p-                                                                            50       16.0   20.0 33.0 18.0 26.0 39.0                             toluoylpyrrole-                                                                          75       18.0   27.0 49.0 30.0 35.0 56.0                             2-acetic acid                                                                            100      29.0   35.0 50.0 42.0 49.0 58.0                             guaiacyl ester                                                                 ______________________________________                                    

Mucolytic activity

The experiment was carried out "in vitro" according to the method of R. S. Hirsch (Bull. Physio-path. resp., 9: 435, 1973) for the purpose of investigating the effect of 1-methyl-5-toluoylpyrrole-2-acetic acid guaiacyl ester on the consistency of human expectoration collected from patients suffering from chronic bronchopulmonary diseases.

Table IV lists the percentage decrease of the expectoration consistency provoked by the compound of this invention in comparison with dithiothreitol and acetylcysteine which are known mucolytic agents.

                  TABLE IV                                                         ______________________________________                                         Mucolytic activity of 1-methyl-5-p-toluoylpyrrole-                             2-acetic acid guaiacyl ester                                                                            No. of  % decrease of                                                          experi- expectoration                                 COMPOUNDS    DOSE        ments   consistency                                   ______________________________________                                         Dithiothreitol                                                                              0.1 M (1.5%)                                                                               12      90                                            acetylcysteine                                                                              1.2 M (20.0%) 12                                                                           81                                                    1-methyl-5-p-toluoyl-                                                                       1.0 M (9%)  12      52                                            pyrrole-2-acetic acid                                                          guaiacyl ester                                                                 ______________________________________                                    

Antitussive activity

The antitussive effect on albino male Guinea-pigs weighing 300 g was evaluated using the method described by Y. Kase (Selected Pharmacological Testing Methods, p. 363, Marcel Dekker Inc., New York, 1968).

                  TABLE V                                                          ______________________________________                                         Antitussive activity of 1-methyl-5-p-toluoyl-                                  pyrrole-2-acetic acid guaiacyl ester.                                          % variations of the kymograph plot concerning                                  amplitude and frequency of coughs                                                            % INHIBITION                                                                   per os     i.p.                                                              DOSE    ampli-  fre-   ampli-                                                                               fre-                                  COMPOUNDS   mg/kg   tude    quency tude  quency                                ______________________________________                                         Tolmetin Na.2H.sub.2 O                                                                     50       0       0      0     0                                    "           75       7       0      0    10                                    "           100      5       5      7    10                                    1-methyl-5-p-toluoyl                                                                       50      16      22     18    26                                    pyrrole-2-acetic                                                                           75      19      45     25    50                                    acid guaiacyl ester                                                                        100     38      56     40    55                                    ______________________________________                                    

Ulcerogenic activity

Male Wistar rats weighing 180 g were randomized into groups of 10. Three doses of each compound were administered. One group received the vehicle alone (10 ml/kg b.w.). Each dose was given orally for four days consecutively and the rats were sacrificed on the fifth day for necropsy. The ulcerogenic effect was evaluated by the following scale:

number of lesions:

(1) each haemorrhagic point at least 1 mm in diameter was scored as 1 lesion,

(2) haemorrhagic points less than 1 mm in diameter were scored in the following manner:

(a) 1 to 9=one lesion

(b) 10 to 19=two lesions

(c) 20 to 29=three lesions

severity of lesions:

(1) no lesion: 0

(2) gastric mucosal irritation without haemorrhage: 1

(3) haemorrhagic points less than 1 mm in diameter: 2

(4) haemorrhagic points between 1 and 3 mm in diameter: 3

(5) haemorrhagic points larger than 3 mm in diameter: 4

(6) perforations 5

By means of this scale it was possible to obtain the gastric damage index: ##EQU2##

The results are given in Table VI.

                  TABLE VI                                                         ______________________________________                                         Ulcerogenic activity of 1-methyl-5-p-toluoylpyrrole-2-acetic acid              guaiacyl ester                                                                                                   %      gastric                                         DOSE    mean No. mean   incidence                                                                             damage                                COMPOUNDS mg/kg   of lesions                                                                              severity                                                                              10     index                                 ______________________________________                                         Vehicle   --      1        1      6       8                                    Tolmetin   50     2        2      7      11                                    Na.2H.sub.2 O                                                                  Tolmetin  100     2.5      3.5    10     16                                    Na.2H.sub.2 O                                                                  Tolmetin  200     3        4      10     17                                    Na.2H.sub.2 O                                                                  1-methyl-5-p-                                                                             50     1        1      7       9                                    toluoylpyrrole-                                                                          100     1        2      8      11                                    2-acetic acid                                                                            200     2        2      8      12                                    guaiacyl ester                                                                 ______________________________________                                    

Toxicity

Acute toxicity of 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester was determined in two animal species, i.e. in albino male Swiss mice (23±1 g) and male Wistar rats (110 g) via the oral and intraperitoneal routes. Table VII lists the LD₅₀ values (mg/kg).

                  TABLE VII                                                        ______________________________________                                         Acute toxicity of 1-methyl-5-p-toluoylpyrrole-                                 2-acetic acid guaiacyl ester                                                                Animal  LD.sub.50 (mg/kg)                                         COMPOUNDS      species   per os  i.p.                                          ______________________________________                                         Tolmetin       Mice        802    550                                                         Rats        827    612                                          1-methyl-5-p-  Mice      >1500   1200                                          toluoylpyrrole-                                                                               Rats      >1500   1175                                          2-acetic acid                                                                  guaiacyl ester                                                                 ______________________________________                                    

The data given in Tables I-VII show the considerable pharmaco-therapeutical effect of 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester at the tested doses and in comparison with the control products. The low toxicity of the above compound confers to it a high therapeutical index: in fact it may be observed that the acute toxicity values (Table VII) are of several magnitudes higher than those used for reaching pharmacologically active doses. Moreover, it is interesting to observe that the ulcerogenic effect is moderate as regards the number of gastric lesions and their severity (Table VI) contrary to antiinflammatory agents in general which produce a marked ulcerogenic effect. Administration to healthy animals at the doses and routes used in the experiments did not provoke death in the long- or short-term treatments nor apparent signs of toxic effects. The results given in Tables I-VII witness the therapeutical interest of the pharmaceutical composition of the present invention.

The patients in need of an antiinflammatory, analgesic, antipyretic, mucolytic and antitussive pharmaceutical composition will be orally or parenterally administered a therapeutically effective amount 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester.

The dose of this compound orally or parenterally administered will be generally comprised between about 2 and about 15 mg/kg of body weight/day, although larger or smaller doses can be administered by the attending physician having regard to the age, weight and general conditions of the patient, utilizing sound professional judgement.

In practice, the compound is orally or parenterally administered in any of the usual pharmaceutical forms which are prepared by conventional procedures well-known to those persons skilled in the pharmaceutical technology. These forms include solid and liquid unit dosage forms such as tablets, capsules, suppositories, solutions, syrups and the like as well as injectable forms, such as sterile solutions for ampoules and phials. Hereinbelow some non-limiting examples of compositions suitable for oral or parenteral administration are given.

    ______________________________________                                         PHARMACEUTICAL COMPOSITIONS                                                    ______________________________________                                         (1) CAPSULE                                                                    Each capsule contains:                                                                               200        mg                                            active principle                                                               excipients:                                                                    starch                48         mg                                            lactose               143        mg                                            magnesium stearate    1.5        mg                                            sodium lauryl sulfate 0.2        mg                                            (2) INJECTABLE PHIAL (3 ml)                                                    Each phial contains:  175        mg                                            active principle                                                               excipients:                                                                    propylene glycol      250        mg                                            sodium metabisulfite  9          mg                                            sodium hydroxide      3.6        mg                                            lidocaine hydrochloride                                                                              10         mg                                            sterile bidistilled                                                            water                 balance to 3                                                                              ml                                            (3) SUPPOSITORY                                                                Each suppository contains:                                                                           200        mg                                            active principle                                                               excipients:                                                                    mixture of triglycerides of                                                                          750        mg                                            vegetal saturated fatty acids                                                  polysorbate           250        mg                                            ______________________________________                                     

What is claimed is:
 1. A compound, 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester having the formula ##STR10##
 2. An orally or parenterally administrable pharmaceutical composition suitable for use as antiinflammatory, analgesic, antipyretic, mucolytic or antitussive comprising a therapeutically effective amount of 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester and a pharmacologically acceptable excipient therefor.
 3. A process for the therapeutic treatment of a patient in need of an antiinflammatory, analgesic, antipyretic, mucolytic and antitussive comprising administering to the patient an amount of 1-methyl-5-p-toluoylpyrrole-2-acetic acid guaiacyl ester effective for such purpose. 